Fix undefined method error

[FixRM rapid7#8347]

Author: wchen-r7

modules/auxiliary/admin/oracle/osb_execqr2.rb

@@ -51,7 +51,7 @@ def run
 				'method' => 'POST',
 			}, 5)
 
-			if (res.headers['Set-Cookie'] and res.headers['Set-Cookie'].match(/PHPSESSID=(.*);(.*)/i))
+			if (res and res.headers['Set-Cookie'] and res.headers['Set-Cookie'].match(/PHPSESSID=(.*);(.*)/i))
 
 				sessionid = res.headers['Set-Cookie'].split(';')[0]